handle plugin buffer response

[FredKSchott]

Changes

• Now we support return Buffer; from plugins
• Resolves issue brought up in Can't return binary strings or buffers from plugin transform() in v2.9 #945

Testing

• Manually tested (We don't have good testing for third party plugins at the moment)

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[gr2m]

I've followed @jaredLunde's "Option 1" instructions here: #945 (reply in thread)

I've run yarn dev and then the local snowpack from this pull request side-by-side, but I don't see any differences. I was expecting to see a different image size? What am I looking for?

[jaredLunde]

@gr2m I updated the plugin to return {result: Buffer} instead of just a binary string so neither option will be broken anymore. Previously the image file was corrupted.

[gr2m]

I have reverted this change directly in node_modules/snowpack-plugin-resize-images/dist/main/index.js. I saw the image being corrupted. But it was still corrupted when I run snowpack dev from this pull request.

Did you check if this pull request fixes the problem for you?

[jaredLunde]

The old plugin returned a binary string. It will still be corrupted w/ this PR because this doesn't attempt to handle binary strings, it just fixes a bug where you couldn't return just a buffer. You had to return an object {result: Buffer}. @stramel covered the issues around handling binary strings in the discussion.

Sequence of events was something like:

1. I try returning a Buffer from my sharp plugin, that doesn't work
2. I convert it a binary string instead, which works in 2.9.0
3. 2.9.1 converts everything to a Buffer, but accidentally breaks support for binary strings in the process
4. I find in the source that I can return a Buffer if I put it in an object under the result key
5. fks submits this PR making it possible to return a Buffer without putting it in an object

[gr2m]

We don't have good testing for third party plugins at the moment, hmm

@FredKSchott could we create a testcase with a minimal plugin local to the test?

[FredKSchott]

@gr2m I'd rather not implement a new test suite as a part of this PR, but I definitely agree that we're overdue. I actually think that testing would be a great place for you to dig into to set up these things for the long term.

Added a note that this has been manually tested